- Implemented but not tested yet
- All existing tests passing

* Not implemented yet. Currently always return false.
* Test exists and compiles, but is failing due to the missing implementation.

- All variables conceptually have an initial value now.
- All initial values read by blocking read() before starting the main loop.
- More tests failing, probably to old test exceptiations and wrong test implementations.

- tests still failing
- modifications incomplete
- cleanup needed

fix not using a ConsumingFanOut when connecting the two poll-types each with a push-type variable (e.g. control system)

this happens frequently when following the modern connectTo() logic and connecting everything with the control system.

rename VersionNumberUpdatingRegisterDecorator into MetaDataPropagatingRegisterDecorator, as it does more than just updating the VersionNumber now

bidirectional variables: pass on version numbers in modules from the last blocking read on to any write operations, to resolve conflicts of concurrent variable updates properly

Added preliminary support for bidirectional variables. There are still some known issues, e.g. concurrent updates can still lead to race conditions. This will be addressed soon.

fixed connectTo() for direct device to control system connections when using the [] operator on the device module

Updated to use the new ReadAnyGroup instead of the old readAny function. Some tests are still hanging or failing (mostly due to shutdown issues)

We have a visitor now for generating
 - the XML
 - the Module's dot graph
 - the textual dump of the VariableNetwork
 - the dot graph of the VariableNetwork

allow determining a fully qualified name for application variables (i.e. including qualified name of owning module)

renamed VariableNetworkNode getTriggerReceiver() into VariableNetworkNode getNodeToTrigger() for better clarity

When attaching a trigger to a node, the resulting triggered node is stored and later returned when the same trigger is attached again to the same node. This fixes crashes when joining two networks sharing the same node triggered by the same trigger, if the triggering node was technically different.

Instead of making the DeviceModule return the same VariableNetworkNode for the same register, an optimisation step before realising the connections (but after all connections have been defined) is performed. In this step, all networks sharing the same (device-type) feeder will be merged. This is more flexible and avoids problems with (potentially different) triggers etc.

Made some exception descriptions more elaborate. To achieve this, the dump() functions have been extended to allow writing to an arbitrary ostream.